The present invention relates to an oscillating-piston engine having a housing with a circular inner wall in which several piston configured as two-armed levers, of which each two adjacent pistons are in rolling engagement with one another, are each arranged pivotably about a piston axis parallel to a central housing axis and are moveable together in a revolution direction, said piston axes revolving about said housing axis on a circular track concentric with said inner wall of the housing.
An oscillating-piston engine of this kind is known from WO 93/01395.
Oscillating-piston engines belong to a species of internal combustion engines in which the individual working strokes, i.e. intake, compression, ignition, expansion, and expulsion of the combustion mixture, are mediated by rocker-like pivoting movements of the individual pistons between two end positions. The pivoting movement of the pistons is converted by corresponding intermediate members into a rotary movement of an output shaft.
In a first embodiment described in the document cited initially, the pistons are arranged in inherently stationary fashion in the housing, and perform only back-and-forth pivoting movements between two end positions. In order to convert the pivoting movements into rotary movements of an output shaft arranged centrally in the housing, the output shaft is joined in fixed-axis fashion to cam follower members, eccentric with respect to the shaft and located diametrically opposite one another, on which the surfaces of the pistons facing the output shaft roll. For this purpose, these piston surfaces facing the output shaft are of defined parabolic configuration, while the cam follower members are cylindrical in shape.
It is viewed as disadvantageous, with this known design for an oscillating-piston engine, that when the pistons are in the dead center positions, i.e. the positions at which a reversal of their pivoting movement takes place, the torque at low engine speeds is small; this is explained by the fact that the pistons are arranged in stationary fashion in the housing.
In a second exemplifying embodiment described in the document cited initially, the pistons not only are mounted pivotably in the housing, but moreover are movable in a revolution direction about the central housing axis.
When this oscillating-piston engine runs, the pistons therefore execute movements which result from a superposition of the rocker-like pivoting movements and the circular revolving movement of the pistons. As compared with the embodiment described earlier, the combined pivoting and revolving movement means that the cam follower members are droplet-shaped in cross section rather than cylindrical, while the surfaces of the pistons facing the output shaft, which is still arranged centrally, have the shape of a quarter-circle. As the pistons revolve, the droplet-shaped cam follower members roll on these surfaces of the piston, and each of the two cam follower members that are present is thereby caused to rotate. The droplet-shaped cam follower members are joined to the output shaft not in fixed-axis fashion but via a gear linkage arranged in the housing, in order to transfer their inherent rotation to the output shaft.
For this purpose, each of the cam follower members has a pinion, joined immovably to it, which is in geared engagement with an idler gear that in turn meshes with a central gear that is mounted on the output shaft.
Although the shape of the torque curve is more favorable with this embodiment than with the embodiment described earlier, this design is technically much more complex. The number of moving parts in this oscillating-piston engine is increased by the fact that now the cam follower members themselves are also rotatably mounted, and that several pinions are provided in order to transfer the rotary movements of the cam follower members to the output shaft.
The cam follower members have the function not only of controlling the pivoting movements of the individual pistons, but also of transferring all the drive force of the pistons to the output shaft. The bearings of the cam follower members must accordingly be of very stable configuration.
In addition, the functionally dictated droplet-shaped profile of the cam follower members is disadvantageous because they taper in relatively pointed fashion, so that as the pistons revolve, when the pistons pass over the tip of the cam follower members there is a "hard" transition between the gently curved and sharply curved rolling regions during rolling. This contributes to a reduction in the smoothness of run of this oscillating-piston engine.
DE Published Application 15 51 101 discloses a centrifugal piston internal combustion engine which has six pistons of approximately triangular shape, spaced apart from one another, which are mounted pivotably on a circular input drive gear in such a way that as they revolve in the housing of the engine, they are pressed by the resulting centrifugal forces against the inner wall of the housing. The pistons are guided independently of one another along the inner wall. In order to achieve the oscillating movements of the pistons, the inner wall of the housing is of approximately oval or trochoidal configuration. Arranged centrally in the housing are two stationary guide cams which ensure, even at low engine speeds at which the centrifugal forces are small, that the pistons are pressed against the inner wall of the housing in order to maintain the functionality of the engine at low engine speeds. The guide cams have no function at high engine speeds.
Also known, from GB Patent 1 470 648, is a rotary piston engine in which a total of four pistons are arranged in the engine housing, each two diametrically opposing pistons forming a piston pair. The inner wall of the housing is of approximately elliptical configuration, the pistons being again, as in the case of the centrifugal piston internal combustion engine cited above, guided along the inner wall as they revolve in the housing in order to achieve the working strokes of the engine. Adjacent pistons are each joined to one another in such a way that the joining points respectively form a seal which is always in contact against the inner wall. Also arranged centrally in the interior of the housing are two stationary cam follower members, elliptically shaped to correspond to the inner wall, on which piston-mounted rollers run in order to press the pistons against the inner wall of the housing. One cam follower member is provided for each piston pair, the two cam follower members being differently configured.